Part built Allchin 1.5 inch

[Former MemberParticipant @formermember19781]

[This posting has been removed]

[derek blakeParticipant @derekblake72550]

Many thanks Bill, everything I’ve posted so far has been on lathe or hand filed this is really the biggest mistake so far and it’s a real kick in the teeth after such effort.

Your right I hope Jason does have an idea, I’m hoping a new valve will save the cylinder being scrap.

Regards

Derek

[Clive Brown 1Participant @clivebrown1]

I'll stick my neck out a bit but I suggest that your error won't be too serious. If the distance between the outer edges of the 2 inlet ports is correct, then basic valve timing will be OK. What you will have is a narrower sealing land between inlet and outlet ports, which might allow a bit more live steam to pass directly to the exhaust. This is not ideal, but not a show stopper.

Others might see it differently.

[derek blakeParticipant @derekblake72550]

Hi Clive

Thank you for your response, hopefully you are correct and it’s still useable. What I’m thinking is if I made a new valve with more material left and thinner exhaust port this would mean that the two side ports wouldn’t be exposed like they are now.

[Paul KempParticipant @paulkemp46892]

Derek,

Don't panic Mr Mainwaring!!! Don't panic. As the overall distance is fine the timing of inlet steam will still be OK (it does look as if the valve has quite a bit of steam lap though). The lap of the valve is the amount the valve overlaps the ports (steam or exhaust). Some engines have a positive lap on the exhaust cavity which leaves a cushion of steam in the cylinder at dead centre but many have negative lap on the exhaust (more commonly termed exhaust clearance). I am sure Jason being very CAD literate and a nice chap could knock up a drawing to asses the impact of what you have now and whether you really need to adjust anything. You will need to give him some decent dimensions though. Overall length of valve (across the ports) the distance between the outer edges of the steam ports, the width of the steam ports, the width of the exhaust port and the size of the ligaments as a check. Overall designed valve travel would be helpful too (throw of the eccentrics would be close enough). I am afraid I am a CAD dunce so it would take me a lot longer to work out than Jason. You could also mock it up in a valve simulator to get an idea of what the effect would be but I struggle with them as well lol.

Paul.

[JasonBModerator @jasonb]

Derek, post the 5 sizes of the ports and gaps and I'll see what size valve cavity would work best with them.

Another option would be to mill out a recess over the ports and let in a plate with the right spacing, though not easy without a mill.

[derek blakeParticipant @derekblake72550]

Hi Jason

Please could you confirm what you need, the overall width of port face with the drilling’s is 15.87mm as per drawing.

The side ports are 2.75mm wide appox, the vains or strips of material down the middle are 2mm wide each instead of the required 2.38mm

The central exhaust port is 6mm instead of 6.35mm.

The width of steam space on valve should be 29/64mm but mine is 11.64mm and I didn’t touch that part it’s from casting so I hadn’t cleaned it up yet.

I’m not sure I’ve given what you ask but ask me what you require.

Many thanks

[derek blakeParticipant @derekblake72550]

[derek blakeParticipant @derekblake72550]

[derek blakeParticipant @derekblake72550]

[JasonBModerator @jasonb]

That's what I needed the size they have come out at, I have the original drawings.

[derek blakeParticipant @derekblake72550]

[derek blakeParticipant @derekblake72550]

[derek blakeParticipant @derekblake72550]

Thank you very much for taking the time everyone to help me.

[JasonBModerator @jasonb]

Think i have got a cure, will post in the morning. But if you want to post the exact 3 opening sizes as you have the overall an dtwo dividers I'll tweak my drawing to suit.

Edited By JasonB on 30/01/2019 20:53:01

[derek blakeParticipant @derekblake72550]

[derek blakeParticipant @derekblake72550]

[derek blakeParticipant @derekblake72550]

[derek blakeParticipant @derekblake72550]

[derek blakeParticipant @derekblake72550]

[JasonBModerator @jasonb]

Right here we go.

First sketch is what you currently have on the top and the book sizes at the bottom with valve at the mid point.

And now at full valve travel. With the large amount of lap and the overall width of the ports not being that different you will get fairly similar running. I would be inclined to leave as is for now.

If you do find it won't run well then it is not too hard to change the valve at a later stage, this has the top valve reduced in overall length an the cavity reduced, at mid point

Part way along the inlet now opens at the same time as the drawing version

And at full eccentric throw

If you do decide to alter it then the overall needs to be 19.78mm and the cavity 10.34mm, you could solder in some metal to reduce the cavity of just make up a new valve from scratch.

[derek blakeParticipant @derekblake72550]

Thank you so much Jason.

I'm really surprised that it would still work with the valve not fully covering the exhaust when in mid point, but that's why I'm not an expert but I do need to learn how it all works.

I will leave alone for now then and see how we go, are you saying that the cylinder block will be fine and the only thing we would need to change is the valve itself? which of course would be a lucky escape for me.

many thanks again for taking time to look into this for me.

[derek blakeParticipant @derekblake72550]

what I have found is the valve casting cavity is actually oversized compared to the drawing anyway, and that was without me even touching it.

I guess the casting just wasn't very good.

[JasonBModerator @jasonb]

Yes the cylinder can be left as it is. You may loose a bit of economy and power but the little Allchin is not the type of engine that is going to be rallied every weekend and expected to do road runs.

[derek blakeParticipant @derekblake72550]

Thanks very much Jason, and everyone else who commented.

[Author]

Posts